1. Field of the Invention
The present invention relates generally to short-range wireless communication systems. More particularly, the present invention relates to an inductively coupled high frequency wireless link between transceiver units for unidirectional or bidirectional transmission of high-fidelity signals.
2. Description of Related Art
Personal entertainment and communication devices continually integrate more functions in a single package, and exploit new user interface concepts. However, less progress has been made in eliminating the ubiquitous headset cord, which is widely regarded as the most cumbersome element of many body-mounted devices. The headset cord reduces freedom of movement, compromises usability and aesthetics, and is usually the first thing to break.
Prior art systems have employed a variety of wireless communication techniques for eliminating the need for a headset cord. Most wireless communication systems generally fall into three categories, depending on the transmission medium employed: ultrasonic, infrared, and radio frequency. Each of these categories exhibits unique performance characteristics, as well as attendant advantages and limitations, well known to those skilled in the art. Ultrasonic communication systems are typically limited to short range applications, and can cover relatively large groups of people. However, they are highly sensitive to interference. Because the signals are in the audio range, discrimination among users is difficult to achieve.
Infrared (xe2x80x9cIRxe2x80x9d) communication systems are generally limited to short range, line-of-sight applications and are generally immune to non-optical forms of interference. Some existing wireless IR systems employ analog frequency modulation (xe2x80x9cFMxe2x80x9d) techniques. However, IR analog FM systems are impractical for on-body use because their transmit power requirements are too high and thus, cannot be supported by a small capacity battery. More importantly, IR systems inherently require an unobstructed line-of-sight between the transmitter and receiver. Such an unobstructed line-of-sight cannot be guaranteed with on-body applications. The transmitted IR signals might be obscured by the user""s body (e.g., arms, shoulder) or attire as a result of normal body movement.
In contrast, radio frequency (xe2x80x9cRFxe2x80x9d) communication systems can transmit over relatively long distances and can employ many different forms of modulation including amplitude modulation (xe2x80x9cAMxe2x80x9d) and frequency modulation (xe2x80x9cFMxe2x80x9d) for transmitting signals via an RF carrier. However, the operating frequency band for transmission must be carefully selected to achieve optimal performance. For example, the use of the commercial FM band in short range wireless communication systems has several disadvantages. Because of the existing high concentration of high-power commercial FM signals in the 88-108 MHz frequency band, users may commonly be located within range of powerful broadcast stations that could overwhelm the front end (RF input circuits) of the user""s receiver, causing undesirable de-sensing and spurious modulation. Also, it may be impossible to prevent stray electric field (xe2x80x9cE-fieldxe2x80x9d) radiation beyond the user""s receiver if the commercial FM band is used. For example, if the intended user receives the desired signal from the body-worn transmitter at a signal-to-noise ratio (xe2x80x9cSNRxe2x80x9d) of 60 dB, a lower quality signal (30 dB SNR) might be audible at tens of meters distant, and would interfere with commercial FM receivers in its vicinity.
Accordingly, a need exists in this industry for a short-range wireless communication system that minimizes or eliminates the deficiencies of the prior art. The many embodiments of the present invention, as described below, satisfy such a need.
An object of the present invention is to provide a wireless communication system that provides small radio coverage xe2x80x9cspheresxe2x80x9d or micro-cells, especially for on-body use.
A further object of the present invention is to optimize the transmission coverage area that also minimizes interference. Specifically, wireless systems according to the present invention should not interfere with other wireless systems in their vicinity. Other related objects of the present invention are to minimize the loss of signal quality in the presence of similar units operating nearby, to facilitate compliance with FCC emission regulations by sharply reducing the field strength of the transmitted electric field, and to eliminate the need for head-mounted controls by implementing a low-speed data network from control unit to earpiece.
Another object of the present invention is to minimize the physical dimensions of the body-worn control unit and head-mounted earpiece to enhance user comfort and convenience.
Still another object of the present invention is to minimize the power consumption of the body-worn control unit and head-mounted earpiece to maximize battery life.
These and other objects are provided by a short range, high-fidelity, stereophonic wireless system with an inductively coupled wireless link suitable for on-body use. The transmitted audio signals exhibit FM broadcast-band quality audio or better. Another embodiment employs analog frequency modulation (xe2x80x9cFMxe2x80x9d) of an HF carrier (3 to 30 MHz) and inductive coupling between a transmitting antenna and a receiving antenna. The body-worn master control unit may be mounted on the belt of the user or other convenient location and the head-mounted slave unit is designed as an earpiece.
In one embodiment, the wireless communication is unidirectional on one channel. The control unit includes one transmitter and each slave unit includes one receiver. Communication between the control unit and the slave unit is accomplished via inductively coupled coils.
In another embodiment, the wireless communication is unidirectional on multiple channels. The control unit includes a plurality of transmitters, preferably two, where each transmitter operates at a distinct carrier frequency associated with a particular slave unit. In this embodiment, the user employs two earpieces (one for each ear) where each earpiece includes a receiver tuned to one of the carrier frequencies of the control unit""s transmitters. Thus, stereophonic transmission is made possible in this two-transmitter, two-receiver configuration. Since two separate carrier frequencies are used for left and right channel audio, fidelity is improved over traditional FM-MPX stereo transmissions used in the FM broadcast band. Communication between the control unit and the slave unit is accomplished via inductively coupled coils.
In a further embodiment, the wireless communication is bidirectional on multiple channels. The control unit includes multiple transmitters and multiple receivers for coupling with one or more transmitters and one or more receivers in each slave unit. Communication between the control unit and the slave unit is accomplished via inductively coupled coils.
In another embodiment, the control unit is coupled to a conventional audio device or electronic device such as a CD player, tape player, commercial FM receiver, cellular telephone, cordless telephone, or a computer system and transmits two channels of high-fidelity audio to the head-mounted earpiece, along with an additional slow-speed digital control channel. The head-mounted earpiece contains a stereophonic receiver that demodulates the signals transmitted from the control unit and outputs high-fidelity audio signals to conventional headphones or other audio transducers. The head-mounted earpiece also decodes the slow-speed digital control channel, which includes commands for receiver configuration, user interface, power control, and channel synchronization. A single voice-band audio signal is modulated onto an HF carrier at the earpiece, and the modulated signal is transmitted from the earpiece to the control unit over the same inductively-coupled communication channel used for stereophonic belt-to-ear communication, as described above. A receiver at the control unit demodulates this additional channel and outputs the resulting audio signal to a transducer or other device. For example, the audio signal may be sent to a computer, cellular phone, or intercom system for further processing or to communicate with other users.
In another embodiment of the present invention, the wireless system uses Faraday shielding techniques, in which the electric field portion of the transmitted electromagnetic field is substantially eliminated during transmission, while the magnetic field portion is substantially unaffected.
A variety of alternate embodiments and optional features of the present invention are described, including (1) bidirectional (xe2x80x9ctwo-wayxe2x80x9d) belt-to-ear connections to facilitate telephony and voice commands, (2) multiple carrier channels with automatic transmitter/receiver synchronization, (3) automatic power control based on audio input and carrier detection, (4) average transmit power reduction using voice-operated relays (xe2x80x9cVOXxe2x80x9d), (5) diversity antenna reception schemes, and (6) advanced wireless control device applications. All system variations of the present invention are adaptable for on-body use, although in some cases additional devices in the user""s environment may also be accessed or controlled (for example, wireless computer workstation audio).
Accordingly, it will be appreciated by those skilled in the art that the present invention provides a short range, inductively coupled, high-fidelity wireless communication system which overcomes many of the problems associated with prior art systems. For example, at VLF, larger coils are needed; also, it is difficult to obtain more than one channel at VLF. The above objects and description of the present invention may be better appreciated with the aid of the following text and accompanying drawings.